Technical Field
Embodiments of the present disclosure relate to a light irradiation device, an image reading device, and an image forming apparatus.
Related Art
Recently, in an image reading device, such as a scanner device, disposed in, e.g., a facsimile machine, a copier, or a multifunction peripheral, there is demand for enhancement of start-up speed, energy saving, light extension, and the like, and a light irradiation device (an original-document lighting device) using a light emitting diode (LED) being a point light source is employed as a light source.
Recent advancement of LED technologies has enabled manufacturing of brighter LEDs, and such a brighter LED can be mounted on a scanner having a high reading rate that requires high illuminance on the surface of original document.
When an illumination system includes an LED having a light emitting surface which is small to be regarded as a point light source, the light intensity may be low, resulting in a non-uniform illuminance distribution in a sub-scanning direction. Hence, in an original-document lighting device using an LED as the light source, a light guide member guiding light from the LED is adopted. In an image reading device in which high image quality is required, it is necessary to optimize the light source such as the LED and the light guide member, to efficiently concentrate light, and to obtain a uniform illuminance distribution. In addition, high light utilization efficiency is preferable for cost reduction.
To enhance the light utilization efficiency, light is preferably concentrated on a read center by the light guide member. As the light guide member, for example, a light guide member including a transparent material, such as a transparent resin including polymethyl methacrylate (PMMA), is used. From the viewpoint of cost reduction, the light guide member is usually manufactured by injection molding which is excellent in mass productivity and is low in cost.
For example, a technology of sandwiching the light guide member is proposed as a light irradiation device allowing an irradiation area to be efficiently irradiated with light.